1. Field of the Invention
This invention pertains to the field of passive component chip termination machines. More particularly, it pertains to a paste recovery system for cleaning the paste recovered from the paste application wheel following the application of paste to the chip.
2. Description of the Prior Art
Passive component chips, such as capacitor chips, or just "chips" are used throughout the computer industry. If they are capacitors, they are small devices made of minute layers of electrically-conductive material separated by like minute layers of dielectric ceramic material where the total size of the chip is smaller than a grain of rice. The conductive layers are electrically joined together by having a silver-based paste applied along opposed edges. The paste, called "termination" is dried and later fired. The chip is soldered directly to the copper traces of a computer mother board to complete the desired circuit therein.
Chips are being improved virtually daily. There is also constant pressure to reduce their overall size. A secondary process overlays the silver termination with a layer of nickel that acts as a barrier to prevent migration of silver ions from the chip to the copper on the circuit board. The nickel layer is then overlayed with a second solder layer for direct soldering to the circuit board. More and different treatments are designed for the chip to make it more efficient, easier to apply to the circuit board, and to make it last longer in the circuit.
One of the latest treatments for chips is to increase the size of the paste blob that is applied to the ends or edges of the chips. This is done for reasons that include a greater reservoir of silver ions to withstand the later nickel and secondary solder treatments. Previously, the aim in chip termination was to place the minimum amount of paste along the end or edge of the chip; now, in certain cases, the opposite is true and more paste is required.
The chip termination machines of the prior art carry the chips in slots and masks formed in a continuous metal belt or carrier. The chip is loaded in the belt at a location remote from the paste application unit and then conveyed thereto in the belt. After application of paste to one end or edge of the chip, the chip is passed through a paste drying oven and then reversed in its position in the slot and mask and conveyed to a second paste application unit where paste is applied to the opposite end or edge and then the chip is again passed through the oven to dry the paste.
In all this handling the chip is liable to move in the mask and not be totally aligned when it is presented to the paste application unit. It is vitally important to have the chip properly aligned in the mask so that the paste covers only a specific portion of the chip. Should the paste be applied in a manner that is not perfectly parallel to the end or edge of the chip, the electrical properties of the chip may be grossly distorted.
It has been the past practice to contact the appropriate end or edge of the chip with a paste termination or application wheel having a paste application circumferential surface that is wider than the end or edge to be terminated. This surface is arranged parallel to the proper orientation of the chip in the carrier belt so that the two come into contact and the chip is aligned or moved into alignment in the mask so that the paste is applied in a parallel band.
With this new requirement for a larger amount of paste to be applied to the chip, the contact between the chip and the circumferential surface on the paste application wheel actually works to the disadvantage because the contact tends to provide sufficient surface tension to the liquid paste to pull off any excess from the chip. Accordingly, there is needed a new design of paste application wheel that will apply a larger glob of paste on the chip while at the same time contacting the chip to align it properly in the mask.
In addition, there is an ongoing problem of some of the chips being pulled out of the masks during contact with the termination or application wheel. This is thought to be the result of the mask losing its gripping power, a thinner than usual chip, or a combination of the two reasons. In any event, the chip finds its way into the paste that is normally scraped off of the wheel and also finds itself becoming mixed with the paste that remains in the reservoir under the application wheel. When these chips become involved with the paste they often become lodged between the wheel and the doctor blade causing lines in the paste pattern on the termination wheel. Accordingly, there remains a problem of removing the chips captured this way from the inventory of paste remaining in the paste application unit to ensure continuous processing of the chips.